ABSTRACT A number of clinically important diseases are caused by pathogens that elicit immunopathologic host responses. Many of these diseases lack suitable experimental models and require high level biocontainment laboratories for their investigation. We have explored a murine model of herpes simplex virus type 2 (HSV-2) vaginal infection to investigate host immunoregulatory mechanisms that effectively balance responses controlling infection with reciprocal responses preventing damage to self. Our data indicates IL-17-mediated inflammation contributes to the development of genital pathology and viral encephalopathy observed upon murine vaginal HSV-2 infection, and that transfer of cells displaying a regulatory T cell phenotype (CD4+CD25+) from HSV-2 infected donors to na[unreadable]ve recipients concomitant with infection inhibits these immunopathological processes without compromising viral clearance. Understanding regulatory T cell (Tregs) mechanisms of activation and migration;antigen specificity;and mechanisms used to regulate immune responses to viral infection are logical next steps in the construction of immunotherapeutics that create acceptable balance between pathology and protection. In Specific Aim 1 we will confirm preliminary data that implicates IL-17 as a cause of the immunopathology associated with murine vaginal HSV-2 infection by identifying the cell types responsible for IL-17 production and determining the pathologic contributions of IL-17- mediated inflammation toward host tissue destruction and viral CNS spread with the use of IL-17 neutralizing antibodies and IL-17 receptor knockout mice. In Specific Aim 2 we test the hypothesis that the decreased genital pathology and death observed in mice receiving transfer of HSV-induced Tregs concomitant with vaginal HSV-2 infection is at least partially mediated by IL-10 production from the transferred population. Highly purified Tregs from Foxp3+ GFP knock-in mice will first be used to confirm that Tregs are in fact responsible for this protective effect. We will also: 1) trace migration and retention of the protective population to the lymphoid organs and genital tracts of na[unreadable]ve and infected recipients;2) use ex vivo capture assays, in vivo neutralization antibodies, and knockout mice to confirm that HSV-induced Tregs can confer protection via production of IL-10;3) determine if the increased protection afforded by the inducible Tregs is the result of HSV-antigen specificity or non-specific activation. In Specific Aim 3 we will test the hypothesis that HSVinduced Tregs decrease genital pathology by both inhibiting harmful IL-17-mediated responses and promoting protective IFN-&#947;-mediated responses by demonstrating transfer of HSV-2 induced Tregs at the time of infection inhibits generation of IL-17-mediated immune responses and polarizes vaginal immunity toward protective IFN- &#947;-mediated innate and adaptive immune responses that serve to facilitate clearance of HSV-2 and establish viral latency. To complete this aim, we will determine if IFN-&#947;dominated immune responses induced by the transfer of Tregs generate memory T cell recall responses that confer protection upon lethal re-challenge.